1. Field of the Invention
The present invention relates to a centrifugal fan in a positive blower, an induced draft fan apparatus or the like, and more specifically, it relates to a technique for holding securely the center of a main plate for supporting blades in line with the rotational axis.
2. Description of the Related Art
FIG. 3 illustrates a conventional centrifugal fan, in which a blade 1 is supported by a main plate 2 and a side plate 3, and said main plate 2 is connected to the rotation shaft 4 by means of a rivet 5.
In the above-mentioned conventional centrifugal fan, however, the main plate 2 may be deformed due to the centrifugal force caused by the rotation of the fan or by hot blast, whereby an excessively strong stress is applied to the connecting part of the main plate 2 and the rotation shaft 4. In order to give an appropriate degree of looseness to the connection, the rivets 5 are used to press the parts together. However, since no other force is applied to the connection, if the stress is greater than the pressing force, the main plate 2 can move freely in relation to the rotation shaft 4, and displacement of the center of the main plate results. This displacement of the center of the main plate has been the most important factor in the vibration of the fan due to balanced mass.